This invention pertains generally to electromagnet actuators and more particularly to such actuators in which the armature is retained against a biasing force in a retracted position by magnetic attraction until selectively released to an actuating or extended position.
Electromagnetic actuators such as relays or print hammers are well known in which a magnetic armature is released from an attracted position by a counteracting bucking coil. The magnetic holding flux in such devices may be generated by a permanent magnet or electromagnetic coils energized by either direct or alternating current. Reset of the armature or actutator is accomplished by terminating the energization of the bucking coil while maintaining the normal holding flux, providing a supplemental flux generator or mechanical reset device.
These actuators frequently comprise a multi-legged core, usually three legs, to provide alternate flux paths along which the primary magnetomotive force can be diverted by the bucking coil to accomplish release of the armature. Although the holding force can be generated by an alternating current coil, the holding flux source is preferably produced by means of a direct current coil or permanent magnet because of the fast operating times, smaller size and low input energy requirements. Examples of A.C. actuators are shown in U.S. Pat. Nos. 2,509,835 and 3,389,310. In each of these, the primary magnetomotive force is provided by an A.C. coil and release or attraction of the armature or actuator is controlled by opening or shorting a secondary coil on the center leg of the core which is operable to divert the holding flux either to or away from the armature. In U.S. Pat. Nos. 1,956,279 and 3,659,238, permanent magnets are employed as one leg of the core member, and bucking coils are attached to another leg to selectively counteract primary holding flux away from the core leg which retains the actuator.
In each of these references, the selectively operable bucking coil must be supplied with an amount of energy sufficient to reduce the flux in the armature or actuator leg of the core, which is usually some constant quantity. In a low duty cycle or low frequency operation, the input energy is of little consequence; however, in applications requiring a high duty cycle or high frequency operation, input energy becomes significant, causing heating or requiring the use of larger, more expensive components to handle the necessary current.